1. Field of the Invention
The present invention relates to a photosensitive polymer and to a chemically amplified photoresist composition containing the same, and more particularly, the present invention relates to a photosensitive polymer which includes a copolymer of alkyl vinyl ether and to a resist composition containing the same.
2. Description of the Related Art
As semiconductor devices become highly integrated, photolithography processes used in the manufacture of such devices must be capable of forming fine patterns. For example, sub-quarter micron or smaller sized patterns are needed for semiconductor memory devices having capacities exceeding 1 Gbit. Accordingly, conventional resist materials have limited applicability since they are utilized in conjunction with krypton flouride (KrF) excimer lasers having wavelengths (248 nm) which are too large for use in the formation of ultra-fine patterns. Thus, new resist materials have been proposed for use in conjunction with an argon flouride (ArF) excimer laser. This is because the ArF excimer laser has a wavelength (193 nm) which is smaller than that of the KrF excimer laser.
Present resist materials designed for use with ArF excimer lasers suffer several drawbacks as compared with conventional resist materials. The most common of these problems are low transmittance and poor resistance to dry etching.
(Meth)acrylate polymers are generally used and widely known as ArF resist materials. The most typical of these resist materials is the poly(methyl methacrylate-tert-butyl methacrylate-methacrylic acid) terpolymer system manufactured by IBM, Inc. However, such polymers exhibit a weak resistance to dry etching.
To obtain an increased resistance to dry etching, a polymer having a backbone composed of an alicyclic compound such as an isobornyl group, an adamantyl group or a tricyclodecanyl group, is used. However, the resulting resist still exhibits an unacceptably weak resistance to dry etching since only a small portion thereof is occupied by alicylic groups.
Also, since the alicyclic compound is hydrophobic, in the case where the alicyclic compound is contained in the terpolymer, a degree of adhesiveness to underlying layers is deteriorated.
In an attempt to solve this problem, the following tetrapolymer has been proposed in which a carboxylic acid group is introduced to the backbone of the polymer (see J. Photopolym. Sci. Technol., 7(3), 507 (1994).): 
However, the resist layer obtained from the polymer having the above structure still exhibits a relatively poor adhesion to underlying layers, as well as a relatively poor resistance to dry etching. Also, the developing solution that is commonly employed during the development process must be diluted before being used.
Alternatively, a methacrylate copolymer having an alicyclic protecting group represented by the following formula has been proposed (see J. Photopolym. Sci. Technol., 9(3), 509 (1996).): 
An adamantyl group for increasing the resistance to dry etching and a lactone group for improving the adhesion characteristic have been introduced to the backbone of the methacrylate copolymer having the above structure. As a result, the resist layer obtained from the polymer having the this structure does exhibit an improved resolution and depth of focus, but the resistance to dry etching is still relatively poor. Also, severe line edge roughness is observed when a line pattern is formed from the resist layer.
Also, the manufacturing cost associated with raw materials used to prepare the copolymer is very high. In particular, the cost of a monomer having a lactone group introduced thereto (to improve an adhesion characteristics) is so prohibitive as to make it difficult to commercially use the monomer.
Another conventional polymer is a cycloolefin-maleic anhydride (COMA) alternating polymer represented by the following formula (see J. Photopolym. Sci. Technol., 12(4), 553 (1999) and U.S. Pat. No. 5,843,624.): 
While the fabrication cost associated with raw materials needed to prepare a copolymer such as the COMA system is low, the yield of the polymer is noticeably reduced. Also, the transmittance of the polymer at short wavelengths, for example, 193 nm, is very low. Further, since such polymers have an alicyclic group in their backbone which is strongly hydrophobic, they have poor adhesion characteristics.
Also, due to the structural characteristics of the backbone, these polymers have a high glass transition temperature of about 200° C. or higher. As a result, it is difficult to carry out an annealing process to remove a free volume present in a resist layer obtained from such polymers. Thus, the resist layer is susceptible to an ambient environment. For example, the resist pattern may suffer a T-top profile. Also, in post-exposure delay (PED), the resist layer exhibits a decrease in stability to an ambient atmosphere, which entails many problems in a variety of processes using the resist layer.